Over the last decade or so, electronic devices responsible for establishing and maintaining wireless connectivity within a wireless network have increased in complexity. For instance, wireless electronic devices now support greater processing speeds and greater data rates. As a by-product of this increased complexity, radio communications techniques have evolved with the emergence of multiple-input and multiple-output (MIMO) architectures.
In general, MIMO involves the use of multiple antennas operating as transmitters and/or receivers to improve communication performance. Herein, multiple radio channels are used to carry data within radio signals transmitted and/or received via multiple antennas. In comparison with other conventional architectures, MIMO architectures offer significant increases in data throughput and link reliability. MIMO architectures may utilize a “smart” antenna concept requiring multiple sets of antennas, especially for wireless network products such as an Access Point (AP). The use of smart antennas may improve the reliability and performance of MIMO communication, which may be accomplished with polarization diversity (e.g., horizontal v. vertical) and/or the spatial diversity (e.g., physical location of the antennas within the AP or beam-forming/beam-switching antennas).
However, one disadvantage of MIMO is that multiple antennas traditionally required more space within the AP, which poses some difficulties as it is preferred for indoor APs to have low visual impact as these devices are generally placed in conspicuous places such as mounted to the ceiling. When design constraints limit the area of the AP, low profile antennas may be used to satisfy one or more design constraints. Low profile antennas are placed within close proximity to a ground plane. When an antenna with a horizontally polarized component and a ground plane operate in parallel and within close proximity to each other, the ground plane effectively short circuits the electric field generated by the antenna. This lowers the feedpoint impedance of the antenna, which reduces the efficiency and bandwidth of the antenna. The ground plane also creates an opposing magnetic field that interacts with the magnetic field of the antenna. Therefore, the impact of utilizing a low profile antenna is that the proximity of the ground plane reduces the useful voltage standing wave ratio (VSWR) bandwidth and lowers the efficiency of the antenna.
It would be advantageous if the impact of the proximity of the ground plane to the low profile antenna was negated and therefore did not impact the antenna's bandwidth.